The following invention relates to a method and apparatus for passivating magnets and magnetic materials and, in particular, to a method and apparatus for passivating magnets and magnetic materials for use in micro-electromechanical systems (MEMS).
Often elements found in microstructures, such as in MEMS devices, require a protective coating. In particular, a magnet used in MEMS device, for example a microactuator, requires an anti-corrosion coating to prevent the degradation of its magnetic properties due to oxidation of the magnetic material and the collection of debris. The need for a protective coating applies to magnets made from a variety of materials including iron, cobalt, Permadur and stainless steel.
Prior art techniques exists for coating magnets to prevent corrosion and degradation. One prior art technique is electroplating, typically using nickel to form a protective coating on the magnet. The prior art electroplating techniques, however, are unsuitable for small magnets used in MEMS devices. First, it is difficult to achieve a conformal coating on such magnets using electroplating especially if the magnets are irregularly shaped. Also, electroplating cannot easily penetrate the pores and holes in the surface of the magnet to achieve a durable coating. As a result, coatings formed using electroplating often have surface bubbles that may later flake off and cause a malfunction in the MEMS device. In addition, the electroplating process causes hydrogen ions or radicals to form in the magnet surface that affect the grain boundary sights of the magnets. Finally, electroplating is generally limited to a few plating materials such as nickel.
Another prior art process for coating magnets is sputtering in which a coating is deposited directly on the surface of the magnet. Sputter deposition, however, is unsuitable for small magnets used in MEMS applications because it requires line of sight processing so that only two sides of the magnet can be coated at a time. Consequently, several processing steps are required to completely coat the magnet which results in a lengthy process and a non-conformal coating.
Another prior art technique for coating magnets is chemical vapor deposition (CVD). The CVD process has the advantage over the other prior art methods of producing a conformal coating. Nevertheless, because the CVD process requires high temperatures that can adversely affect the magnetic properties of magnetic materials, the CVD process is not suitable for MEMS-based magnets.
Accordingly, it is desirable to provide a system and method for providing a conformal protective coating for small magnets and magnetic materials that is suitable for MEMS devices.
The present invention is directed to overcoming the drawbacks of the prior art. Under the present invention an apparatus and method is provided for uniformly coating a magnet having a plurality of surfaces and includes a reaction chamber having a port for introducing the magnet into the reaction chamber. A heater is also included for heating the reaction chamber. Also, a carrier gas port is in fluid communications with the reaction chamber for introducing a carrier gas into the reaction chamber. In addition, a reactant gas port is in fluid communications with the reaction chamber for introducing a reactant gas into the reaction chamber. When the magnet and the carrier gas are introduced into the reaction chamber, the magnet becomes suspended in the reaction chamber. Also, when the reactant gas is introduced into the reaction chamber, the reactant gas causes all of the plurality of surfaces of the magnet to be uniformly coated.
In an exemplary embodiment, an RF source adjacent the reaction chamber is included so that when the reactant gas is introduced into the reaction chamber, the RF source causes plasma initiated chemical reaction to occur.
In another exemplary embodiment, a UV light source adjacent said reaction chamber is included so that when the reactant gas is introduced in the reaction chamber, the UV light source causes an optically activated chemical reaction to occur.
Accordingly, an apparatus and method is provided for applying a conformal protective coating on small magnets and magnetic materials. In particular, the apparatus and method of the present invention may be used to protectively coat magnets that are used MEMS devices such as disc drive microactuators.
The invention accordingly comprises the features of construction, combination of elements and arrangement of parts that will be exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims. Other features and advantages of the invention will be apparent from the description, the drawings and the claims.